Um, not possible.
I've heard that too and I have to believe that whoever came up with that idea never had anything to do with a truly wide horse. That might be possible on a well-withered narrow horse that has a lot to hold the saddle on with but on a mutton-withered wide horse, good luck buddy!
I mean, both of Lacey's saddles fit her great (they both could be a hair wider in a perfect world but there's really no such thing as too wide with Lacey, she has them all beat in the wide department so there's no such thing as "a hair wider") but I'm in trouble if I tried to ride without a breastcollar and crupper over hilly terrain. On flat ground, they're fine sans attachments but on the hills, oh boy.
And without a mounting block, forget getting on without pulling the saddle over! Even fully cinched up.
She just doesn't have much for the saddle to "grab" on to. I'm pretty sure that the reason I don't know anything about her mother is that her mother was literally a barrel and her conception was an act of God.
I would probably fully die if I tried to mount up from the ground without doing up her cinch/girth...
Speaking of saddle fit, (Bailey's super cute by the way!!) that saddle you have on Bailey looks a little snug in the shoulder area. Boy, do I know that issue! Is it FQHB? If it's not FQHB, I might try try a FQHB on her just to see. Just thought I'd mention it... :)